Down syndrome, also known as Trisomy 21, is a genetic disorder characterized by the presence of a full or partial extra copy of chromosome 21. It is one of the most common chromosomal abnormalities, affecting approximately 1 in every 700 births globally. The condition was first described by John Langdon Down in 1866, hence the name. While the exact causes remain largely unknown, advancements in genetics have illuminated the underlying mechanisms and diagnostic possibilities. This answer will detail the genetic basis, phenotypic manifestations, diagnostic approaches, and management of Down syndrome. Genetic Basis Down syndrome primarily arises from three genetic mechanisms: Trisomy 21: The most common form (95% of cases), where an individual has three copies of chromosome 21 instead of the usual two. This usually occurs due to non-disjunction during meiosis (cell division during gamete formation). Translocation: A portion of chromosome 21 becomes attached to another chromosome (4% of cases). This can be inherited from a parent who carries a balanced translocation. Mosaicism: Some cells have the extra chromosome 21, while others do not (1% of cases). This occurs due to an error during early cell division after fertilization. Phenotypic Characteristics Individuals with Down syndrome exhibit a range of physical and developmental characteristics, which vary in severity. Common features include: Physical Features: Flattened facial features, upward slanting eyes (palpebral fissures), small ears, a protruding tongue, and small hands and feet. Developmental Delays: Cognitive impairment, delayed speech development, and motor skill delays. Associated Health Issues: Increased risk of congenital heart defects (around 50%), hearing loss, vision problems, and gastrointestinal abnormalities. Diagnosis Down syndrome can be diagnosed prenatally and postnatally: Prenatal Diagnosis: Screening tests (e.g., Non-invasive Prenatal Testing - NIPT) and diagnostic tests (e.g., Chorionic Villus Sampling - CVS, Amniocentesis). NIPT, based on cell-free fetal DNA in maternal blood, is increasingly common. Postnatal Diagnosis: Based on physical characteristics and confirmed by karyotyping (chromosome analysis). Management Management focuses on early intervention and supportive care: Early Intervention Programs: Physical therapy, speech therapy, occupational therapy, and educational support. Medical Management: Addressing associated health issues like heart defects and vision problems. Parental Support: Providing counseling and resources for families. Diagnostic Method Description NIPT Non-invasive prenatal testing; analyzes fetal DNA in maternal blood. CVS Chorionic villus sampling; involves taking a sample of tissue from the placenta. Amniocentesis Amniocentesis; involves taking a sample of amniotic fluid. Down syndrome is a complex genetic condition with varying degrees of phenotypic expression. While there is no cure, early diagnosis and comprehensive management, including supportive therapies and medical interventions, can significantly improve the quality of life for individuals with Down syndrome and their families. Continued research into the genetic mechanisms and potential therapies remains crucial for further advancements in care and understanding.

Down's Syndrome: Anthropological Perspective | UPSC Mains ANTHROPOLOGY-PAPER-I 2015

Down's Syndrome.

How to Approach

This question requires a concise yet comprehensive explanation of Down syndrome. The approach should be to first define the condition, its genetic basis, phenotypic characteristics, and associated medical considerations. Subsequently, briefly discussing diagnostic methods and management strategies will complete the answer. Structurally, an introduction defining Down syndrome, a body detailing its genetics, features, diagnosis, and management, and a concluding summary will be adopted. The focus should be on clarity and conciseness within the word limit.

Genetic Basis

Down syndrome primarily arises from three genetic mechanisms:

Trisomy 21: The most common form (95% of cases), where an individual has three copies of chromosome 21 instead of the usual two. This usually occurs due to non-disjunction during meiosis (cell division during gamete formation).
Translocation: A portion of chromosome 21 becomes attached to another chromosome (4% of cases). This can be inherited from a parent who carries a balanced translocation.
Mosaicism: Some cells have the extra chromosome 21, while others do not (1% of cases). This occurs due to an error during early cell division after fertilization.

Phenotypic Characteristics

Individuals with Down syndrome exhibit a range of physical and developmental characteristics, which vary in severity. Common features include:

Physical Features: Flattened facial features, upward slanting eyes (palpebral fissures), small ears, a protruding tongue, and small hands and feet.
Developmental Delays: Cognitive impairment, delayed speech development, and motor skill delays.
Associated Health Issues: Increased risk of congenital heart defects (around 50%), hearing loss, vision problems, and gastrointestinal abnormalities.

Diagnosis

Down syndrome can be diagnosed prenatally and postnatally:

Prenatal Diagnosis: Screening tests (e.g., Non-invasive Prenatal Testing - NIPT) and diagnostic tests (e.g., Chorionic Villus Sampling - CVS, Amniocentesis). NIPT, based on cell-free fetal DNA in maternal blood, is increasingly common.
Postnatal Diagnosis: Based on physical characteristics and confirmed by karyotyping (chromosome analysis).

Management

Management focuses on early intervention and supportive care:

Early Intervention Programs: Physical therapy, speech therapy, occupational therapy, and educational support.
Medical Management: Addressing associated health issues like heart defects and vision problems.
Parental Support: Providing counseling and resources for families.

Diagnostic Method	Description
NIPT	Non-invasive prenatal testing; analyzes fetal DNA in maternal blood.
CVS	Chorionic villus sampling; involves taking a sample of tissue from the placenta.
Amniocentesis	Amniocentesis; involves taking a sample of amniotic fluid.

Additional Resources

Key Definitions

Non-disjunction

The failure of chromosomes to separate properly during cell division (meiosis), leading to an abnormal number of chromosomes in the resulting cells.

Mosaicism

A condition in which an individual has two or more genetically distinct cell populations originating from a single zygote.

Key Statistics

Approximately 50% of individuals with Down syndrome are born with congenital heart defects. [Source: American Heart Association, knowledge cutoff]

Source: American Heart Association

The prevalence of Down syndrome is approximately 1 in 700 births globally. [Source: World Health Organization, knowledge cutoff]

Source: World Health Organization

Examples

Project SEARCH

Project SEARCH is an international program that provides employment opportunities for individuals with disabilities, including those with Down syndrome. It fosters vocational skills and independence.

Frequently Asked Questions

▶Can Down syndrome be inherited?

While most cases of Down syndrome are not inherited, translocation Down syndrome can be passed down from a parent who carries a balanced translocation.

Down's Syndrome.

Model Answer

Introduction